The use of bone plate and screw systems for treatment of bone fractures is widespread. Conventional bone plate and screw systems promote healing of a fracture by compressing the fracture ends together and drawing the bone fragments into close apposition with each other. If the plate is not provided with the appropriate hole types adapted to receive the proper screw types, then the angular relationships between the plate and screws may change postoperatively. This can lead to malalignment and poor clinical results.
Among the various different types of bone plate holes that are known in the art are the two different types of holes described below, each hole primarily intended for use with a different type of bone screw.
The first type of hole is a non-threaded relatively smooth hole, through which a screw with a smooth (non-threaded) head is inserted. These screws do not lock with the bone plate and are thus referred to as “non-locking” screws. Because non-locking screws do not lock with the plate hole, non-locking screws are not limited to a fixed angle with respect to the plate, but rather can be inserted at numerous angles. Inserting non-locking screws through the non-threaded plate holes and threading them into the bone effectively provides the desired compression of fracture ends.
The second type of hole is an internally threaded hole, which is adapted to mate with a screw having an externally threaded head. The threaded-head or “locking” screw is inserted at a fixed, predetermined angular relationship (determined by the central axis of the threaded hole) with respect to the bone plate. Locking screws, when mated with threaded bone-plate holes, possess high resistance to shear and torsional forces. Locking screws therefore resist loosening and thereby ensure stability between the screw and the bone plate.
Bone plates having both of the aforementioned types of holes are therefore desirable and are well known. Surgeons are limited, however, by the manufacturers' placement of the varying holes on a given bone plate. A surgeon can achieve optimal compression when using a screw (e.g., a non-locking screw) without locking it to the plate. A surgeon can achieve desired stability between the screw, plate, and bone when using a locking screw with an internally-threaded hole.
It would thus be advantageous for a hole in a bone plate to be adapted to receive, at the surgeon's election, either non-locking screws for obtaining optimal compression or locking-screws for obtaining optimal stability, while minimizing any compromise in the strength of the bone plate.